Of course your "logical side" is correct. The chance of transmission of HIV, HCV, or anything else is too low to worry about. Drying indeed markedly reduces whateverl miniscule risk there might have been otherise.
Still, I'm glad you asked. Massage parlors need to prevent this sort of thing, regardless of how fragile a customer's skin might be. Workers need to know how (and how not) to use implements like brushes in a way that does not cause injury or potential contact with blood. They also should disinfect such implements between use on different customers. There likely are state or local laws or regulations that govern these things. Even though your risk is too low to warrant testing or ongoing worry, it would be reasonable to phone your local health department and tell them what happened. They might do nothing at all; but for all you know, you could be the latest among several such concerns, in which case they might take action, such as visiting the site to assure that brushes indeed are disinfected between customers (depending on those local laws and regulations).
Good luck-- HHH, MD
Thank you for your feedback, Dr. HHH. I don't live in Nevada and was just visiting on a quick vacation. I will have to look up the health department number and will give them a call when I get a chance. It would be interesting to see what kind of measures are enforced in Las Vegas regarding this kind sanitary concerns.